I am currently trying to build a rig under $450 and this is my newest attempt. My budget is currently low but the future I will hopefully make some upgrades. I want to be able to in the future upgrade easily without having to start all over.
I plan in the future to crossfire, I understand the 6750 is not the best to crossfire together but I can get different videocards when I upgrade later. I need a rig to play steam games and moba's nothing crazy like bf3.
My first suggestion would be to get 2x4g ram 3 sticks will kind of defeat the purpose of dual channel. I also think you could squeeze a better graphics card into that budget. I recently build a gaming computer in this price range, and i got a 7850 into it. Mostly looks ok though.